1. Field of the Invention
The present invention relates to a backlight device and particularly to an edge light type backlight device for use in a liquid crystal display (LCD) or the like.
2. Description of Related Art
An LCD device comprises, for example, a liquid crystal display panel and a backlight system mounted under the liquid crystal display panel for supplying light beams thereto. The backlight system mainly comprises a light source and a light guide plate, wherein the light guide plate is made of a transparent acrylic plastic, and is used for guiding the light beams emitted by the light source to uniformly illuminate the liquid crystal display panel.
The light source emits light beams into the light guide plate, wherein the light beams are totally internally reflected. In order to diffuse the light beams and emit them uniformly from a top surface of the light guide plate, protrusions or recesses are located on a bottom surface of the light guide plate, or a pattern of light diffusion dots are formed on the bottom surface of the light guide plate.
Referring to FIG. 7, a conventional backlight system 9 comprises a light source 40, which can be a light emitting diode, a miniature bulb, or another kind of point light source, a cage 30 having a reflective coating (not shown) thereon, a light guide plate 10, and a translucent sheet 20. The cage 30 has a locating notch 31 therein. The light guide plate 10 comprises a light input surface 11 and a light output surface 12.
In assembly, the light source 40 is arranged in the locating notch 31 of the cage 30, and the light guide plate 10 is accommodated in the cage 30. The light input surface 11 of the light guide plate 10 is adjacent to the light source 40. The translucent sheet 20 is placed upon the light guide plate 10.
In operation, light beams emitted by the light source 40 pass through the light input surface 11 and enter the light guide plate 10, and then are transmitted out from the light output surface 12 of the light guide plate 10. After that, the light beams pass through the translucent sheet 20 to illuminate an LCD panel.
However, the light source 40 has a certain emitting angle. For example, a light emitting diode used as the light source 40 emits light beams with an emitting angle in a range of 30° to 130°. Since the light input surface 11 is planar, when the light beams emitted by the light source 40 impinge on the light input surface 11, they are partly reflected, and partly transmitted. Not all the light beams enter the light guide plate 10. Thus the efficient utilization of the light beams is decreased, and the brightness of the light guide plate 10 is also decreased.
It is desirable to provide an improved backlight system for a liquid crystal display, which overcomes the above problems.